Ok, I just tried it using that script on my site and it's there...can you try one quick thing?
Put this in it instead, publish the page, see if it renders you get the alert popup?
(assuming jQuery is on your page, if not make it $telerik.$(document).ready
So the attachment is that I just tried on my site (granted with v2800) and it rendered okay...there's not anything else wrong right? Like you can make changes to it, it saves, you can publish and go back and the changes are there? If you drop another new widget on the page that renders okay?